Gold futures fell 6.4% to settle at $1,285.9 an ounce -- its lowest level since September 2010.

The drop extended an ongoing sell-off in the precious metal as investors prepare for an end of the Federal Reserve's stimulus policies, which Bernanke said could begin later this year and culminate in 2014.

The CME Group is raising initial margins for Comex gold and NYMEX platinum futures, effective after the close of business Friday.

The parent of the Chicago Board of Trade is raising Comex 100 Gold Futures (GC) initial margins for speculators by 25 percent, to $8,800 per contract from $7,040. Platinum futures NYMEX (PL) initial margins for speculators will rise 12.5 percent, to $3,465 per contract from $3,080.

Like werewolves and vampires, bacteria have a weakness: silver. The precious metal has been used to fight infection for thousands of years — Hippocrates first described its antimicrobial properties in 400 bc — but how it works has been a mystery. Now, a team led by James Collins, a biomedical engineer at Boston University in Massachusetts, has described how silver can disrupt bacteria, and shown that the ancient treatment could help to deal with the thoroughly modern scourge of antibiotic resistance. The work is published today in Science Translational Medicine.

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